Solar System Log by Andrew Wilson, published 1987 by Jane's Publishing Co. Ltd.

Helios 1 was a joint German-American deep-space mission to study the main solar processes and solar-terrestrial relationships. Specifically, the spacecraft's instruments were designed to investigate phenomena such as solar wind, magnetic and electric fields, cosmic rays, and cosmic dust in regions between Earth's orbit and approximately 0.3 AU from the Sun.

It was the largest bilateral project to date for NASA, with the Federal Republic of Germany (FRG, aka West Germany) paying about $180 million of the total $260 million cost. The FRG provided the spacecraft and NASA the launch vehicles. Experiments were provided by scientists from both FRG and the U.S.

After a successful launch, Helios 1 passed within 47 million kilometers of the Sun at a speed of 238,000 km per hour on 15 March 1975, the closest any human-made object had been to our nearest star. During its mission, the spacecraft spun once every second to evenly distribute the heat coming from the Sun, 90 percent of which was reflected by optical surface mirrors. Its data indicated the presence of 15 times more micrometeorites close to the Sun than there are near Earth.

Helios 1's data was correlated with the Interplanetary Monitoring Platform (IMP) Explorers 47 and 50 in Earth orbit, the Pioneer solar orbiters, and Pioneers 10 and 11 en route to leaving the solar system. Control was maintained from a German center outside of Munich. Data was received until late 1982.

Key Dates

10 Nov 1974: Launch

Status: Successful

Fast Facts

Helios 1 set flew closer to the Sun than any other spacecraft of its generation.

Helios was the Greek god of the Sun (right).

Found that micrometeorites are 15 times as plentiful near the Sun as they are at Earth's distance.